Heat exchanger

ABSTRACT

The heat exchanger uses multi-layer tubes, performing efficient heat exchange. Each heat transfer tube includes an outer tube and an inner tube. Header unit directs first fluid through gaps between the inner tube and the outer tube from outer circumferences of the inner tube. The header units are stacked in a top-bottom direction with gap-forming members therebetween, leaving predetermined gap portion. Furthermore, a header cover directs the second fluid through the inner tubes extending from the header units, and is fitted from the outer side, and the second fluid is introduced. With this configuration, the second fluid flowing from the header cover is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions, enabling heat exchange to be performed from both inside and outside of the outer tubes.

TECHNICAL FIELD

The present invention relates to a heat exchanger including left and right headers and heat transfer tubes provided between the headers, and more specifically, it relates to a heat exchanger with improved heat exchange efficiency achieved by making fluid flow over a radially outside of the heat transfer tubes along the axial direction.

BACKGROUND ART

Conventionally, various heat exchangers using multi-layer tubes have been proposed. FIG. 8 shows the structure of a typical heat exchanger having multi-layer tubes. In FIG. 8, reference numeral 83 denotes a coaxial tube that includes an outer tube 84 and an inner tube 85 coaxially provided therein. Examples of such multi-layer tubes include a multi-layer tube in which a large number of fins are provided on the outer circumference of an inner tube along the axial direction, and a multi-layer tube in which a spiral fin is provided on the outer circumference of an inner tube (PTLs 1 to 3). When heated fluid is cooled using such a coaxial tube, the heated fluid is directed through the inside of the inner tube 85, and cold fluid is directed through a gap between the outer tube 84 and the inner tube 85, thereby cooling the fluid in the inner tube 85.

Furthermore, another heat exchanger using multi-layer tubes and having the structure shown in FIG. 9 is also known (PTL 4). In FIG. 9, reference numerals 210L and 210R denote headers provided on the left side and the right side, and reference numeral 210 denotes coaxial heat transfer tubes provided between the left and right headers 210L and 210R. The heat transfer tubes 210 each include an inner tube 211 and an outer tube 212 that are coaxially provided. The inner tubes 211 extend from the outer tubes 212, and fluid subjected to heat exchange is introduced into the inner tubes 211 from the header 210L defined by a header wall 213. On the other hand, portions near ends of the outer tubes 212 are sealed by partition plates 214. Cold fluid is introduced into spaces enclosed by the header walls 213 and the partition plates 214, from which the cold fluid flows into gap regions enclosed between the inner tubes 211 and the outer tubes 212.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.     2005-083667 -   PTL 2: Japanese Unexamined Patent Application Publication No.     2007-163092 -   PTL 3: Japanese Unexamined Patent Application Publication No.     2008-69993 -   PTL 4: Japanese Unexamined Patent Application Publication No.     H07-133993

SUMMARY OF INVENTION Technical Problem

However, when heat exchange is performed using such multi-layer tubes, the following problem occurs: that is, in the heat exchangers illustrated in FIGS. 8 and 9, because fluid subjected to heat exchange is directed through the narrow inner tubes, if a high flow rate is to be ensured, the diameter of the inner tubes needs to be increased. However, if the diameter of the inner tubes is increased, heat exchange is performed only at the outer surfaces of the inner tubes, resulting in a problem of decreased heat exchange efficiency.

Hence, the present invention has been made to overcome the above-described problem, and an object thereof is to provide a heat exchanger that performs heat exchange using multi-layer tubes and can perform efficient heat exchange, even when a high flow rate is to be ensured.

Solution to Problem

More specifically, the present invention has been made to overcome the above-described problem, and it provides a heat exchanger using heat transfer tubes each including an outer tube and an inner tube, the heat exchanger performing heat exchange between first fluid flowing through a gap between the outer tube and the inner tube and second fluid flowing through the inner tube. The heat exchanger includes header units that direct the first fluid through the gaps between the inner tubes and the outer tubes from the outer circumferences of the inner tubes, the ends of the inner tubes extending from the outer tubes; second headers that direct second fluid through the inner tubes extending from the header units; and gap portions provided between the stacked header units, through which the second fluid from the second headers flows. The second fluid from the second headers is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions.

More specifically, the heat exchanger includes header units each holding portions near ends of the outer tubes at a first wall and allowing the inner tubes, which extend from the outer tubes, to extend through a second wall facing the first wall, the header units directing the first fluid through the gaps between the inner tubes and the outer tubes from a space enclosed by the first wall and the second wall; second headers that direct the second fluid through the inner tubes extending from the second walls of the header units; and gap portions provided between the stacked header units, through which the second fluid from the second headers flows. The second fluid from the second headers is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions.

With this configuration, the first fluid flowing through the gaps between the outer tubes and the inner tubes can be cooled or heated by the second fluid from both inside and outside. Thus, the heat exchange efficiency can be improved.

Furthermore, in this invention, the gap portions are provided by disposing gap-forming members between the stacked header units.

With this configuration, a change in size of the gap portions can be achieved by changing the thickness of the gap-forming members. Thus, gaps of an appropriate size can be easily provided.

Alternatively, projections or recesses are formed as an integral part of the header units, and the gap portions are provided utilizing the spaces between the projections and the recesses.

With this configuration, the gap portions can be provided only by staking the header units having the projections or recesses. Thus, bonding the gap-forming members in an assembly process is eliminated.

Moreover, splitting members extending along the axial direction of the heat transfer tubes are provided between upper and lower heat transfer tubes of the stacked header units.

With this configuration, the second fluid flowing via the gap portions can be split and directed toward the surfaces of the heat transfer tubes via the splitting members. Thus, the second fluid can be directed near the surfaces of the heat transfer tubes, thereby improving the heat exchange efficiency.

Furthermore, the splitting members are provided in contact with the heat transfer tubes of the stacked header units, and the second fluid flowing from the gap portions is split and directed toward the heat transfer tubes.

With this configuration, the gap portions may be formed by disposing the splitting members between the heat transfer tubes of the header units, and thermal diffusion can also be performed by making the splitting members in contact with the heat transfer tubes.

Advantageous Effects of Invention

The present invention provides a heat exchanger using heat transfer tubes each including an outer tube and an inner tube, the heat exchanger performing heat exchange between first fluid flowing through a gap between the outer tube and the inner tube and second fluid flowing through the inner tube, the heat exchanger including header units that direct the first fluid through the gaps between the inner tubes and the outer tubes from the outer circumferences of the inner tubes, the ends of the inner tubes extending from the outer tubes; second headers that direct second fluid through the inner tubes extending from the header units; and gap portions provided between the stacked header units, through which the second fluid from the second headers flows. The second fluid from the second headers is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions. Thus, the first fluid flowing through the gaps between the outer tubes and the inner tubes can be cooled or heated by the second fluid from both inside and outside, and the heat exchange efficiency can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a heat exchanger according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along line A-A in FIG. 1.

FIG. 3 is a schematic cross-sectional view taken along line B-B in FIG. 1.

FIG. 4 is a perspective view illustrating a portion near a header according to a first embodiment.

FIG. 5 is a diagram illustrating projections of header units according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating other projections of the header unit according to the second embodiment of the present invention.

FIG. 7 is a schematic view of a heat exchanger according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a heat exchanger using conventional multi-layer tubes.

FIG. 9 is a diagram illustrating a heat exchanger using conventional multi-layer tubes.

DESCRIPTION OF EMBODIMENTS First Embodiment

An embodiment of the present invention will be described below with reference to the drawings. As illustrated in FIG. 1, a heat exchanger 1 according to this embodiment is configured to include first headers 2 a that direct fluid (first fluid) subjected to heat exchange through gaps between inner tubes 41 and outer tubes 42, and second headers 2 b, provided on the outer sides of the first headers 2 a, that direct second fluid through the inner tubes 41. Characteristically, the first headers 2 a each include a plurality of header units 21 stacked, leaving gap portions W thereabove and therebelow, and the second fluid is directed through the gap portions W to perform cooling or heating from both outside and inside of the outer tubes 42, along the axis direction of heat transfer tubes 4. Hereinbelow, the configuration of the heat exchanger 1 according to this embodiment will be described in detail.

The structure of the first headers 2 a constituting this heat exchanger 1 will be described. The first headers 2 a are each formed by stacking the header units 21 holding the heat transfer tubes 4, each including the inner tubes 41 and the outer tube 42. As illustrated in FIG. 4, each header unit 21 is formed of an upper unit segment 22 and a lower unit segment 22, which form a pair and face each other in a top-bottom direction. First recesses 28 a having a shape corresponding to the contour of a halved outer tube 42 are provided in a first wall 23, to which portions near the ends of the outer tubes 42 are attached, and second recesses 28 b having a shape corresponding to the contour of a halved inner tube 41 are provided in a second wall (rear surface 26) axially facing the first wall 23, and the outer tubes 42 and the inner tubes 41 are disposed therebetween. Separation planes 20 in the first wall 23 and the second wall 26 are parallel to the axial plane of the heat transfer tubes 4 arranged in a row, and open portions of the first recesses 28 a and the second recesses 28 b are located in the separation planes 20. Furthermore, a side surface and a bottom surface continuous with the first wall 23 and the second wall 26 are provided, and, an opening 27 is provided in a position where one side surface should be, from which the first fluid is introduced. When the header units 21 are formed using the thus-configured unit segments 22, the unit segments 22 are made to face each other in the top-bottom direction, the portions near the ends of the outer tubes 42 are disposed between the first recesses 28 a, the portions near the ends of the inner tubes 41 extending therefrom are disposed between the second recesses 28 b, and the first fluid is introduced into the spaces between the outer tubes 42 and the inner tubes 41. When the header units 21, in which the heat transfer tubes 4 are sandwiched in this manner, are stacked, gap-forming members 8 are used to provide predetermined gap portions W in the top-bottom direction, and in this state, header covers 3 a that cover the openings 27 in the header units 21 are attached, and the first fluid is introduced from an inlet port 31 a provided therein. When the gap portions W are provided by using the gap-forming members 8, the gap-forming members 8 having a thickness corresponding to the gap width are prepared and attached to the top surfaces or bottom surfaces of the header units 21 to form the gaps.

Next, the structure of the second headers 2 b will be described. The second headers 2 b are configured to direct the second fluid through the inner tubes 41 extending from the second recesses 28 b, and in this embodiment, the second headers 2 b are formed of a single header cover 3 b that covers the first headers 2 a and the header covers 3 a. In this embodiment, the header cover 3 b has a case-like structure that completely covers the first headers 2 a on the left and right sides and the heat transfer tubes 4 therebetween, and the second fluid is introduced from an inlet port 31 b and discharged from an outlet port 32 b (see FIG. 1) provided at both ends thereof. When the second fluid is introduced via the inlet port 31 b in the thus-configured second header 2 b, the second fluid flows into the inner tubes 41 from ends thereof, and the second fluid flowing from the gap portions W between the header units 21 flows along the outer circumferences of the outer tubes 42.

In each heat transfer tube 4, two inner tubes 41 are internally in contact with the outer tube 42 such that their axial planes are aligned. With this configuration, even when the inner tubes 41 expand due to an increase in pressure, the inner tubes 41 internally come into contact with the inner surface of the outer tube 42, and the expansion of the inner tubes 41 can be prevented. When such heat transfer tubes 4 are to be formed, in order to improve the heat exchange efficiency, for example, the outside diameter of the outer tubes 42 is set from about 0.8 mm to 2.0 mm, and more preferably, from about 0.9 mm to 1.5 mm, and the inside diameter thereof is set from about 0.7 mm to 1.9 mm, and more preferably, from about 0.8 mm to 1.4 mm.

Furthermore, splitting members 9 are attached to the upper and lower heat transfer tubes 4 of the header units 21 arranged in a stack. The splitting members 9 are provided in contact with the outer circumferences of the heat transfer tubes 4, so that the second fluid flowing through the gap portions W is split and directed toward the outer circumferences of the heat transfer tubes 4. That is, without the splitting members 9, the second fluid flowing through the gap portions W flows through the gap spaces where no heat transfer tubes 4 are provided, which decreases the heat exchange efficiency. Hence, the splitting members 9 are provided in the gap spaces where heat exchange does not need to be performed, thereby directing the second fluid toward the heat transfer tubes 4 to disperse the heat from the heat transfer tubes 4 and improving the heat exchange efficiency. When the splitting members 9 are attached in this manner, as illustrated in FIGS. 2 and 3, the splitting members 9 are attached parallel to the header units 21 arranged in a stack so as to overlap the gap portions W, as viewed from the axial direction of the heat transfer tubes 4.

Next, advantages obtained when the thus-configured heat exchanger 1 is used will be described.

First, when the first fluid is introduced from the inlet port 31 a in the first header 2 a, the first fluid flows via the header cover 3 a into the header units 21, from which the first fluid is split and flows along the spaces between the outer tubes 42 and the inner tubes 41.

Furthermore, at the same time, the second fluid is introduced from the inlet port 31 b in the second header 2 b. The second fluid then flows from the space enclosed by the header cover 3 b into the inner tubes 41 and flows along the axial direction of the inner tubes 41. Furthermore, the second fluid not flowing into the inner tubes 41 flows in the axial direction of the heat transfer tubes 4 via the gap portions W between the header units 21. Then, the second fluid is split by the splitting members 9 provided in the gaps between the heat transfer tubes 4 and directed toward the upper and lower heat transfer tubes 4, and the second fluid in contact with the outer surfaces of the heat transfer tubes 4 cools or heats the first fluid.

As described above, in this embodiment, the header units 21 are stacked with the predetermined gap portions W therebetween, and the second fluid is made to flow along the axial direction of the heat transfer tubes 4 from the gap portions W. Thus, heat exchange can be performed over the entire heat transfer tubes 4.

Furthermore, because the splitting members 9 in contact with the surfaces of the heat transfer tubes 4 are provided along the axial direction in this embodiment, it is possible to direct the second fluid flowing from the gap portions W toward the surfaces of the heat transfer tubes 4 to further improve the heat exchange efficiency.

Second Embodiment

Next, a second embodiment of the present invention will be described. In the above-described first embodiment, the gap portions W are provided using the gap-forming members 8. In the second embodiment, as illustrated in FIGS. 5 and 6, projections 25 a or recesses 25 b are formed on top surfaces or bottom surfaces of the header units 21, and the second fluid is directed through the gaps therebetween. Note that, in this embodiment, components denoted by the same reference numerals as those in the first embodiment have the same configurations as those in the first embodiment.

The unit segments 22 constituting the header units 21 according to this embodiment have projections 25 a standing upright from the lower side of the bottom surface so as to have a certain thickness, and recesses 25 b between the projections 25 a, thereby forming the gap portions W. Herein, the projections 25 a are formed as an integral part of the unit segments 22 when the unit segments 22 are produced. As illustrated in FIG. 5, the projections 25 a interfere with the upper and lower projections 25 a when the header units 21 are stacked in a top-bottom direction. Thus, when the width of the gap portions W is set to d, the height of the projections 25 a is set to d/2, so that a gap width of d is achieved when the projections 25 a interfere with the upper and lower projections 25 a.

Alternatively, as illustrated in FIG. 6, the projections 25 a may be formed of thin plates extending along the axial direction of the heat transfer tubes 4, and the upper and lower projections 25 a may be arranged so as to overlap each other. In this configuration, the opening 27 in the upper header unit 21 and the opening 27 in the lower header unit 21 are displaced from each other by the thickness of the plate, but the gaps may be filled with a brazing material when the header covers 3 a are attached to the openings 27.

As described above, in the second embodiment, because the projections 25 a (or the recesses 25 b) are formed as an integral part of the header units 21, there is no need to attach the gap-forming members 8 when the header units 21 are stacked. Thus, the task in a stacking process can be simplified.

Although the recesses 25 b are formed between the projections 25 a by forming the projections 25 a in this embodiment, conversely, the recesses 25 b may be formed by removing the bottom surface portion of the unit segment 22, so that the projections 25 a are formed between the recesses 25 b.

Third Embodiment

Next, a third embodiment will be described. Although the gap portions W are provided by the gap-forming members 8 or the projections 25 a in the above-described first and second embodiments, in this embodiment, as illustrated in FIG. 7, the gap portions W may be formed by the splitting members 9 disposed between the upper and lower heat transfer tubes 4. Note that, also in this embodiment, components denoted by the same reference numerals as those in the first embodiment have the same configurations as those in the first embodiment.

The heat exchanger 1 according to this embodiment is configured without the gap-forming members 8 illustrated in FIG. 4, and thick splitting members 9 are mounted between the heat transfer tubes 4 extending between the left and right header units 21 so as to be in contact with the heat transfer tubes 4, thereby providing the gap portions W between the upper and lower header units 21.

The splitting members 9, which are formed of metallic members having a high thermal conductivity, are in contact with the surfaces of the heat transfer tubes 4 to disperse the heat of the heat transfer tubes 4 and to split and direct the second fluid flowing from the gap portions W toward the heat transfer tubes 4 to be subjected to heat exchange.

Note that, when the splitting members 9 are formed of metallic rigid members, the gap between the upper and lower header units 21 is determined by the thickness of the splitting members 9, and if the heat transfer tubes 4 are deformed or when the thickness of the splitting members 9 is inaccurate, the width of the gap between the header units 21 changes. When the gap width changes, the positions of the openings 27 in the header unit 21 change, making it difficult to attach the header covers 3 a thereto. Hence, the splitting members 9 may be formed of, for example, metallic elastic structures, or, only upper and lower surfaces may be formed of metallic members and a layer therebetween may be formed of an elastic material that is relatively elastic, such as urethane. With this configuration, the deformation of the heat transfer tubes 4 may be absorbed owing to the elasticity, making it easy to position the header covers 3 a with respect to the openings 27 when the header covers 3 a are attached to the openings 27.

Note that the present invention is not limited to the above-described embodiments, but may be embodied in various other forms.

For example, although the splitting members 9 are configured to be parallel to the stacked header units 21 and are disposed between the heat transfer tubes 4 in the above-described embodiments, when a high heat exchange rate can be ensured without the splitting members 9, the splitting members 9 do not have to be attached.

Furthermore, although two inner tubes 41 are provided in a circular outer tube 42 in the above-described embodiments, the outer tube may have any shape, and the number of inner tubes may be any value. That is, any shape and any number may be employed, as long as the first fluid is subjected to heat exchange from both inside and outside.

REFERENCE SIGNS LIST

-   -   1 heat exchanger     -   2 header (2 a: first header, 2 b: second header)     -   3 a, 3 b header cover     -   4 heat transfer tube (41: inner tube, 42: outer tube)     -   8 gap-forming member     -   9 splitting member     -   21 header unit     -   22 unit segment     -   23 first wall     -   25 a projection     -   25 b recess     -   26 second wall (rear surface)     -   41 inner tube     -   42 outer tube     -   W gap portion 

1. A heat exchanger using heat transfer tubes each including an outer tube and an inner tube, the heat exchanger performing heat exchange between first fluid flowing through a gap between the outer tube and the inner tube and second fluid flowing through the inner tube, the heat exchanger comprising: header units that direct the first fluid through the gaps between the inner tubes and the outer tubes from the outer circumferences of the inner tubes, the ends of the inner tubes extending from the outer tubes; second headers that direct second fluid through the inner tubes extending from the header units; and gap portions provided between the stacked header units, through which the second fluid from the second headers flows, wherein the second fluid from the second headers is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions.
 2. A heat exchanger using heat transfer tubes each including an outer tube and an inner tube, the heat exchanger performing heat exchange between first fluid flowing through a gap between the outer tube and the inner tube and second fluid flowing through the inner tube, the heat exchanger comprising: header units each holding portions near ends of the outer tubes at a first wall and allowing the inner tubes, which extend from the outer tubes, to extend through a second wall facing the first wall, the header units directing the first fluid through the gaps between the inner tubes and the outer tubes from a space enclosed by the first wall and the second wall; second headers that direct the second fluid through the inner tubes extending from the second walls of the header units; and gap portions provided between the stacked header units, through which the second fluid from the second headers flows, wherein the second fluid from the second headers is directed through the inside of the inner tubes and over outer surfaces of the outer tubes along the axial direction via the gap portions.
 3. The heat exchanger according to claim 1, wherein the gap portions are provided by disposing gap-forming members between the stacked header units.
 4. The heat exchanger according to claim 1, wherein the gap portions are formed by projections or recesses that are formed as an integral part of the header units.
 5. The heat exchanger according to claim 1, wherein splitting members that split and direct the second fluid flowing from the gap portions toward the heat transfer tubes are provided between the heat transfer tubes of the header units.
 6. The heat exchanger according to claim 1, wherein splitting members that are in contact with the heat transfer tubes and split and direct the second fluid flowing from the gap portions toward the heat transfer tubes are provided between the heat transfer tubes of the header units.
 7. The heat exchanger according to claim 2, wherein the gap portions are provided by disposing gap-forming members between the stacked header units.
 8. The heat exchanger according to claim 2, wherein the gap portions are formed by projections or recesses that are formed as an integral part of the header units.
 9. The heat exchanger according to claim 2, wherein splitting members that split and direct the second fluid flowing from the gap portions toward the heat transfer tubes are provided between the heat transfer tubes of the header units.
 10. The heat exchanger according to claim 2, wherein splitting members that are in contact with the heat transfer tubes and split and direct the second fluid flowing from the gap portions toward the heat transfer tubes are provided between the heat transfer tubes of the header units. 